Layers, coatings or films synthesized using precursor layer exerted pressure containment

ABSTRACT

Systems and methods are described for synthesis of films, coatings or layers using precursor exerted pressure containment. A method includes exerting a pressure between a first precursor layer that is coupled to a first substrate and a second precursor layer that is coupled to a second substrate; forming a composition layer; and moving the first substrate relative to the second substrate, wherein the composition layer remains coupled to the second substrate.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 09/957,132, filed Sep.20, 2001 now U.S. Pat. No. 6,500,733 and claims a benefit of priorityunder 35 U.S.C. 120 from all of copending U.S. Ser. No. 09/957,132,filed Sep. 20, 2001; U.S. Ser. No. 09/957,207, filed Sep. 20, 2001; U.S.Ser. No. 09/957,050, filed Sep. 20, 2001; U.S. Ser. No. 09/957,123,filed Sep. 20, 2001; U.S. Ser. No. 09/957,125, filed Sep. 20, 2001; andU.S. Ser. No. 09/957,121, filed Sep. 20, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of materials. Moreparticularly, the invention relates to synthesis of layers, coatings orfilms. Specifically, a preferred implementation of the invention relatesto the synthesis of layers, coatings or films using precursor layerexerted pressure containment. The invention thus relates to a layer,coating or film synthesis technology of the type that can be termedprecursor layer pressure contained.

2. Discussion of the Related Art

A plethora of methods have been used for the synthesis of films(coatings) composed of materials from the CIS (copper indium selenide)material system and related alloys, but each of the previous methods hascharacteristics that limit their applicability to the economicalmanufacture of films with properties suitable for application tooptoelectronic devices, such as photovoltaic (PV) devices. PV devicesrequire an optical absorber that also provides sufficiently longminority carrier lifetimes to enable the collection of the minoritycarriers by the electrodes in the device's structure without excessiverecombination. In all semiconductor materials minority carrier lifetimesare dependent on the defect structure of those materials. The control ofdefect structure is critical to the successful manufacture of PVdevices. Similarly the defect structure of high-temperaturesuperconductors, electroluminescent phosphors, and other(opto-)electronic materials control the physical properties thatdetermine their efficacy for their respective intended uses.

Thin film optical absorbers are more economical than thick filmabsorbers or coatings because they require a smaller amount of theprecursor materials than thick films or coatings. The formation of thinfilms with desirable defect properties is predominately determined bythe method by which they are synthesized. Early efforts to fabricatethin film CIS PV devices that relied on the steady-state co-depositionof the constituent elements copper, indium, and selenide were not verysuccessful¹. The first efficient thin film CIS PV devices were achievedby a two-step process that relied on the sequential deposition of twolayers onto a substrate at high temperature, each with differentcomposition. These layers reacted and intermixed to yield a nominallyuniform composition throughout their combined thickness, and resulted infilms with desirable defect structures²⁻⁴. Variations of this methodhave been demonstrated, based on different temperatures, numbers oflayers, and compositions thereof.^(5,6). Other fundamentally differentapproaches have been described that rely on, for example: (1) heatingstacked layers of the metals (e.g., copper, indium and gallium) andselenide that have been sequentially deposited at low temperatures⁷⁻⁹,(2) thermal reaction of metallic layer precursors in hydrogenselenide^(10,11) or selenide vapor¹², (3) thermal reaction of oxideparticulate precursor mixture layers at high temperatures¹³, and (4)thermal reaction of binary (Cu,Se) and (In,Se) precursor layers^(14,15).

An economical process for the manufacture of thin films of these sortsof non-stoichiometric multinary compounds needs to both efficiently useraw materials and be rapid (for low cost), but must be flexible toenable control of the defect structures required for high performance.None of the methods in the prior art provide an optimal combination ofthese features. Heretofore, the requirements of efficient raw materialutilization, rapid fabrication, and flexibility for optimization ofdefect properties referred to above have not been fully met. What isneeded is a solution that simultaneously addresses all of theserequirements.

SUMMARY OF THE INVENTION

There is a need for the following embodiments. Of course, the inventionis not limited to these embodiments.

According to an aspect of the invention, a method comprises: exerting apressure between a first precursor layer that is coupled to a firstsubstrate and a second precursor layer that is coupled to a secondsubstrate; forming a composition layer; and moving the first substraterelative to the second substrate, wherein the composition layer remainscoupled to the second substrate. According to another aspect of theinvention, a method comprises: applying an electrostatic field across afirst precursor layer that is coupled to a first substrate and a secondprecursor layer that is coupled to a second substrate; forming acomposition layer; and moving the first substrate relative to the secondsubstrate, wherein the composition layer remains coupled to the secondsubstrate. According to another aspect of the invention, a methodcomprises: locating a template within at least one of a first precursorlayer that is coupled to a first substrate and a second precursor layerthat is coupled to a second substrate; forming a composition layer; andmoving the first substrate relative to the second substrate, wherein thecomposition layer remains coupled to the second substrate. According toanother aspect of the invention, a method comprises: providing asurfactant as an impurity within at least one of a first precursor layerthat is coupled to a first substrate and a second precursor layer thatis coupled to a second substrate; forming a composition layer; andmoving the first substrate relative to the second substrate, wherein thecomposition layer remains coupled to the second substrate. According toanother aspect of the invention, an apparatus comprises: a first holder;a second holder coupled to the first holder; a linkage coupled to thefirst holder and the second holder to move the first holder relative tothe second holder; a reusable tool coupled to the first holder, thereusable tool including a raised patterned surface; and a release layercoupled to the raised patterned surface of the reusable tool. Accordingto another aspect of the invention, a composition comprises: acomposition layer defining a first surface and a second surface, thecomposition layer including a collection layer that is located closer tothe first surface than to the second surface.

These, and other, embodiments of the invention will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingvarious embodiments of the invention and numerous specific detailsthereof, is given by way of illustration and not of limitation. Manysubstitutions, modifications, additions and/or rearrangements may bemade within the scope of the invention without departing from the spiritthereof, and the invention includes all such substitutions,modifications, additions and/or rearrangements.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings accompanying and forming part of this specification areincluded to depict certain aspects of the invention. A clearerconception of the invention, and of the components and operation ofsystems implemented the invention, will become more readily apparent byreferring to the exemplary, and therefore nonlimiting, embodimentsillustrated in the drawings, wherein like reference numerals designatethe same elements. The invention may be better understood by referenceto one or more of these drawings in combination with the descriptionpresented herein. It should be noted that the features illustrated inthe drawings are not necessarily drawn to scale.

FIGS. 1A-1D illustrate schematic side views of a subgeneric process toproduce a composition layer on a substrate, representing an embodimentof the invention.

FIGS. 2A-2D illustrate schematic side views of a process to produce aCIS absorber layer on an electrode coated substrate, representing anembodiment of the invention.

FIGS. 3A-3D illustrate schematic side views of a pressure containmentutilizing process to produce a CIGSS layer on an electrode coatedsubstrate, representing an embodiment of the invention.

FIGS. 4A-4B illustrate schematic side views of an electrostatic fieldutilizing process to produce a CIGSS layer on an electrode coatedsubstrate, representing an embodiment of the invention.

FIGS. 5A-5B illustrate schematic side views of a template utilizingprocess to produce a CIGSS layer on an electrode coated substrate,representing an embodiment of the invention.

FIGS. 6A-6B illustrate schematic side views of a surfactant utilizingprocess to produce a CIGSS layer on an electrode coated substrate,representing an embodiment of the invention.

FIG. 7 illustrates a schematic sectional view of a PV device thatincorporates an absorber layer formed on an electrode coated substrate,representing an embodiment of the invention.

FIG. 8 illustrates a schematic elevational view of a system thatincorporates a plurality of PV devices shown in FIG. 7.

FIGS. 9A-9B illustrate top and expanded sectional views, respectively,of a release layer coated tool, representing an embodiment of theinvention.

FIG. 10 illustrates a schematic view of an hexagonal array of releaselayer coated tools, representing an embodiment of the invention.

FIG. 11 illustrates a schematic cross view of a manufacturing systemthat includes a release layer coated rotating cylindrical tool,representing an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention and the various features and advantageous details thereofare explained more fully with reference to the nonlimiting embodimentsthat are illustrated in the accompanying drawings and detailed in thefollowing description. Descriptions of well known starting materials,processing techniques, components and equipment are omitted so as not tounnecessarily obscure the invention in detail. It should be understood,however, that the detailed description and the specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only and not by way of limitation. Various substitutions,modifications, additions and/or rearrangements within the spirit and/orscope of the underlying inventive concept will become apparent to thoseskilled in the art from this disclosure.

Within this application several publications are referenced bysuperscript Arabic numerals. Full citations for these, and other,publications may be found at the end of the specification immediatelypreceding the claims. The disclosures of all these publications in theirentireties are hereby expressly incorporated by reference herein for thepurpose of indicating the background of the invention and illustratingthe state of the art.

The specification of this application is similar to U.S. Ser. No.09/957,207, filed on Sep. 20, 2001 (attorney docket no. HELE:003US) U.S.Ser. No. 09/957,050, filed on Sep. 20, 2001 (attorney docket no.HELE:004US); U.S. Ser. No. 09/957,123 filed on Sep. 20, 2001 (attorneydocket no. HELE:005US); U.S. Ser. No. 09/957,125 filed on Sep. 20, 2001(attorney docket no: HELE:006US), and U.S. Ser. No. 09/957,121, filed onSep. 20, 2001 (attorney docket no. HELE:007US); the entire contents ofall of which are hereby expressly incorporated by reference herein forall purposed.

The below-referenced U.S. Patents disclose embodiments that weresatisfactory for the purposes for which they are intended. The entirecontents of U.S. Pat. No. 4,392,451 to Mickelsen, et al., issued Jul.12, 1983; U.S. Pat. No. 4,523,051 to Mickelsen, et al., issued Jun. 11,1985; U.S. Pat. No. Re. 31,968 to Mickelsen, et al., reissued Aug. 13,1985; U.S. Pat. No. 5,396,839 to Tuttle, et al., issued Oct. 18, 1994;U.S. Pat. No. 5,436,204 to Albin, et al., issued Jul. 25, 1995; U.S.Pat. No. 5,441,897 to Noufi, et al., issued Aug. 15, 1995; U.S. Pat. No.5,567,469 to Wada, et al., issued Oct. 22, 1996; U.S. Pat. No. 5,578,503to Karg, et al., issued Nov. 26, 1996; and U.S. Pat. No. 5,674,555 toBirkmire, et al., issued Oct. 7, 1997 are hereby expressly incorporatedby reference herein for all purposes.

In general, the context of the invention can include the fabrication ofa composition layer, coating or film that may be used in a subassembly,which may in-turn be used in a larger assembly. The context of theinvention can include the fabrication of a semiconductor layer, coatingor film for use in, for example, a photovoltaic device and/or system.The context of the invention can also include the fabrication of asuperconductor layer, coating or film for use in, for example, anelectronic or electrical device and/or system.

The invention solves the problems in the prior art approaches discussedabove by providing precursor layers on different surfaces which are thenplaced into contact with one another. The precursor layers can then beinteracted chemically and/or physically to produce the compositionlayer. The surfaces can be defined by one or more substrates and/or oneor more tools. The substrate(s) and/or tool(s) can each define one, ormore than one, surface onto which the precursor substance is deposited.The substrate(s) and/or tool(s) can be compliant, thereby improvingcontact between the precursor layers, improving pressure control,structure transfer and/or surface behavior during interaction of theprecursor layers.

Preferred embodiments of the invention deposit two different precursorlayers onto two different substrates, or on a substrate and a tool, oreven on two different tools. The deposited precursor layers are thencontacted together. The contacted precursor layers can then subsequentlyinteract under the influence of motion, heat, pressure, electrostaticfields, (quasi)epitaxial forces, surfactants, magnetic fields and/orcatalysts. At least a part of one of the substrates can then bemodified. The composition layer can remain coupled to the othersubstrate. Modifying can include removing, by etching and/or mechanicalmotion. It may be desirable not to modify a portion of the firstsubstrate, for example not remove that portion so that it remains on thecomposition layer. The surfaces can then be moved relative to oneanother resulting in release of the unified layer(s) from one of theoriginal surfaces and/or adhesion of the unified layer(s) to only one ofthe original surfaces.

FIGS. 1A-1D show a sequence of process steps. In FIG. 1A, a firstsubstrate 110 is coupled to a release layer 120. The release layer 120is coupled to a first precursor layer 130. A second substrate 140 iscoupled to a second precursor layer 150. In FIG. 1B, the first precursorlayer 130 and the second precursor layer 150 have been brought intocontact so they can interact directly. The contact is preferablyintimate to establish and maintain a planar interaction front. In FIG.1C, a composition layer 160 has resulted from the interaction. In FIG.1D, the first substrate 110 and the release layer 120 have been movedaway from the composition layer 160 which remains on the secondsubstrate 140.

The invention can include the formation of a collection layer 170,preferably located between the composition layer 160 and the secondsubstrate 140. The location of the collection layer 170 away from a freesurface 161 of the composition layer 160 can be an important aspect ofthe invention. The function of the collection layer 170 can be tosequester undesirable material, preferably in a safe location. Thecollection layer 170 (which can also be termed a collection zone) can bepositioned away from sensitive device locations such as semiconductorregions. The collection layer can include undesirable material such asexcess precursor(s), secondary phase precipitates, impurities, residueand/or debris. The collection layer 170 can provide a physical signatureor fingerprint that can be detected and/or characterized withinassemblies (devices) that incorporate the composition layer 160. Thecollection layer 160 can make a determination of whether an electronic(e.g., photovoltaic) device infringes the claimed invention relativelyeasy.

The interaction between the precursors layers can be chemical (e.g.,reactants forming a product) and/or physical (e.g., two polymersintermingling to form a copolymer or two metals diffusing together toform a solid solution). The invention is more flexible than the priorart approaches described previously because it allows separateoptimization of the composition, structure, and deposition processes forthe precursor (e.g., reactant) layers apart from the optimization of thechemical and/or physical reaction used to form the composition layer(e.g., a chemical product layer in the form of a final film).

It is desirable that the compositions of the two precursor layers besuch that a difference of melting point temperature exists between themso that one of them may be heated to its melting point temperaturewithout melting the other. This enables a thin-film liquid-solidreaction process, which can be controlled by the application of motion,heat, pressure, electrical bias, templates, and/or surfactants betweenthe compliant substrate and reusable tool to yield layers, coatingand/or films with the desired composition (and gradients thereof),structure and defect distributions.

These precursor structures (e.g., layers) are different from thosepreviously described in the art because they are designed in pairs, onefor deposition onto each of the two surfaces (e.g., tool surface andsubstrate surfaces). The substrate upon which the unified compositionlayer is formed by the interaction of the pair of precursors can remainas part of an assembly containing the composition layer.

The other substrate can be a reusable tool composed of, for example,silicon. The working surface of the reusable tool can be coated with arelease layer composed of, for example, calcium fluoride, strontiumfluoride and/or their alloy (Ca,Sr)F₂. Such a reusable tool can be usedto apply pressure, as a counter-electrode for electrical biasing, and/oras a crystallographic template to control the structure of the precursorstructure grown thereupon, can be recharged with subsequent precursorstructures, optionally on a continuous basis.

The invention can include the fabrication of the precursor layer(s) onthe substrate(s). For instance, the precursor layers can be fabricatedby sputtering followed by plasma discharge, particle deposition,physical vapor deposition and/or chemical vapor deposition. In apreferred embodiment, one or both of the precursor layers can befabricated by sputtering of an elemental metal (e.g., copper) followedby plasma discharge of another element (e.g., elemental selenide vapor).

The invention can include subsequent processing of the compositionlayer. For instance, the composition layer can be post-process heated inan atmosphere (e.g., air or oxygen) to tailor the defect structureand/or improve performance. This post-processing heating in anatmosphere can be termed annealing.

The invention can include devices that incorporate the resultingcomposition layer(s) (e.g., PV devices that contained the compositionlayer as an absorber layer(s)). Further, the invention can also includesystems that include such devices. The invention can include equipmentfor forming the composition layer(s).

The following example uses the copper-indium-selenide (CIS) materialsystem and material systems formed by the addition of gallium (CIGS),sulfur (CISS), or aluminum (ACIS), and/or combinations thereof (e.g.,CIGSS, ACIGSS, etc.). The use of these material systems is merelyexemplary of the methods described herein and is not intended to suggestthat the invention is limited to these material systems. The generalproperties of these materials that render the invention applicable willbe described in enabling detail.

FIGS. 2A-2D depict a process sequence used to make a CIS material layer.In FIG. 2A, a reusable tool 210 is coupled to a calcium fluoride releaselayer 220. The calcium fluoride release layer 220 is coupled to anindium selenide precursor layer 230. A compliant substrate 240 iscoupled to a molybdenum electrode 245. The molybdenum electrode 245 iscoupled to a copper selenide precursor layer 250. In FIG. 2B, the indiumselenide precursor layer 230 and the copper selenide precursor layer 250have been brought into intimate contact. In FIG. 2C, a chemical reactionproduct layer 260 (CIS) has resulted from the interaction. In FIG. 2D,the reusable tool 210 and the calcium fluoride release layer 220 havebeen moved away from the chemical reaction product layer 260 whichremains on the compliant substrate 240.

In this example, CIS films are formed by the deposition of binary coppermonoselenide onto a molybdenum-coated substrate and indiumsesquiselenide onto a calcium fluoride-coated silicon substrate. Sincethe substrates are separate, the deposition of these precursor layerscan be done at different temperatures. When these composites are broughttogether under mechanical pressure and rapidly heated to an appropriatetemperature of above approximately 520° C. but below approximately 635°C., only the copper monoselenide layer will melt.

Sufficient mechanical pressure can substantially prevent the loss ofselenide vapor from the reaction zone, thereby achieving highlyefficient incorporation of selenide into the composition layer (in thisexample, a chemical product layer). In this example, the pressure shouldbe from approximately 0.01 atm to approximately 10.0 atm, preferablyfrom approximately 0.2 atm to approximately 1.0 atm if sulphur issubstantially not present. Other examples that do not use copperselenide may not need as much pressure.

In this example, the adhesion of the resulting CIS film to themolybdenum will be substantially stronger than its adhesion to thecalcium fluoride release layer and the resulting CIS film will onlyadhere to the molybdenum-coated substrate, permitting reuse of thecalcium fluoride-coated silicon substrate as a reusable tool. In thisexample, the final thickness of the CIS film can be from approximately0.5 microns to approximately 3.5 microns, preferably from approximately1.0 microns to approximately 3.0 microns.

The invention can include the use of an electrostatic field appliedacross the first precursor layer and the second precursor layer.

The application of a voltage between the molybdenum film (or underlyingsubstrate carrier) and the silicon wafer (which bears the calciumfluoride coating), with the electrostatic potential of the silicon waferhigher than that of the molybdenum film, will tend to retard thetransport of positive copper ions into and through both the indiumsesquiselenide layer and the resulting adjacent indium-rich CIS layerthat is formed during the reaction. The calcium fluoride release coatingis an insulator, thereby preventing current flow between the precursorlayers and establishing the electrostatic field.

This will assist in maintaining a planar reaction front. This will alsoassist in minimizing composition fluctuations by providing a negativefeedback mechanism to inhibit the formation of dendritic structuresduring the reaction. The electric field applied can be fromapproximately 0.03 volts/micron to approximately 3.5 volts/micron,preferably from approximately 0.3 volts/micron to approximately 1.0volts/micron. It can be appreciated that the electric field can generatea significant force between the first precursor and the secondprecursor, thereby adding to pressure that is otherwise exertedmechanically. Further, the overall pressure can be controlled (e.g.,modulated) without mechanical manipulation by changing the appliedelectric field.

The electrical bias during the synthesis process can be applied in alarge number of ways and the optimal technique will depend on thedetails of the materials used for the various parts. If the releaselayer is an electrically insulating material and the reusable toolconductive, the bias is preferably applied between the electrode layerand the tool. The closer that the biased surfaces are brought togetherthe higher the electric field strength across the precursor layersduring the synthesis process for any given potential difference betweenthose electrodes. In any case it is desirable that there is at least onenon-conducting layer separating the biased electrodes so that electricalcurrent does not flow between them when their precursor layers arebrought into contact with one another.

The use of an electrical bias between the upper and lower substratesduring heating and precursor interaction can have a number of beneficialeffects. First, a static potential difference will always create anattractive force between the precursors that will serve to insure theirintimate contact during heating. A static potential difference can beused to control the pressure in the reaction zone itself, an elementaryconsequence of electrostatic field theory.

The tendency of the electric field to planarize the reaction frontbetween the binary precursors used in the preferred embodiment for CISsynthesis is a more subtle consequence of the fact that their reactionproduct, CIS, is substantially less electrically conductive than eitherof the precursors themselves. As a consequence, any perturbation thatcreates curvature at the interface between a relatively conductivebinary precursor and CIS locally increases the electric field intensity.If the direction of that field inhibits diffusion of the ionicreactants, the reaction front will be slowed in proportion to the localcurvature. This self-moderation effect (negative feedback) tends toplanarize the reaction front, and its relevance to the synthesis of acomposition layer by this method is contingent only on (1) thecomposition (e.g., product) being substantially less conductive than theprecursors (e.g., reactants), and (2) the existence of at least oneionic specie that must transport out of a precursor layer, in thisexample to react and lead to formation of the product material. Notethat in the context of condensed state material physics the phrase ionicspecie, as used herein, is defined as an entity which feels a force inthe presence of an electric field. Of course, the polarity of theelectrostatic field can be reversed. As an initial configurationparameter, during the interaction and/or modulated during theinteraction.

There can be explosive kinetics involved. The electrostatic field can beused to control the reaction trajectory. It may be desirable to reversethe field in different parts of the process. It is possible to use thereverse bias to slow down the diffusion of copper. It is also possibleto reverse an initial electrostatic field over part of the reactioncycle, to force copper out at a faster rate, thereby changing thekinetics by changing the relative attachment rate to thecrystallographic front, of copper and selenide. This can be termedforward bias. The invention can include incorporating selenide into thelattice from the melt. But the selenide does not have a crystallographicguiding force or a chemical guiding force to attach to that surface,unless one is also transporting copper into it. If the selenide isallowed to attach faster than the copper, a phase transition would thenoccur that could cause solidification within that liquid layer. Fasterselenide attachment involves a shift over to the side of the binaryphase diagram where the dominant stable specie is di-copper selenide,Cu₂ Se. In contrast, with slower selenide attachment the dominant stablespecie is closer to CuSe. By reverse biasing, the diffusion of copperinto the indium-selenide layer can be inhibited. A build up of copper inthat layer occurs faster than rolling up the selenide. It is undesirableto move toward the Cu₂Se side of the phase diagram and precipitate solidCu₂Se crystals. The field can be used to control the relative transportrate. In this example, the interaction is a transport-related reaction.The desired crystalline properties are propagated up toward the toollayer by, among other things, solid state diffusion of copper. The solidstate transports but it is not necessarily diffusive transporting.Diffusive transport is governed by the diffusion equation so that italways ends up with a straight line profile for composition. However,non-diffusive transport is possible. An example is convection.Convection is characterized by a first order differential equationrather than a second. With a field-assisted transport, an intermediatecase is acquired, which depends on the field strength. That intermediatecase, depending on the direction of the field, can either inhibit thecopper transport or, accelerate it. The injection of copper into thatsurface will lead to a restructuring process. Therefore, a higher coppercontent at the front can be desirable. If the front copper content ishigh enough, it will have already caused a transformation from hexagonalto FCC stacking. That is the desirable crystallographic front to whichthe copper transporting through the indium selenide should attach. Analternating field as well as a static field, or combinations thereof maybe used to create the electric bias. By modulating a reversal of thefield, the reaction trajectory can be controlled, optionally in a timedomain manner.

The invention can include the use of a structure transfer layer orsubstance. These structure transfer layer(s) and/or substance(s) can betermed a template. The template can be used to transfer the morphologyof one layer to another. The template can be used to transfermeta-symmetry from one layer to another. The template can be used toepitaxially transfer a lattice structure from one layer to another.

As an example of a template layer, the invention can include putting arelatively group 1 rich template film (e.g., copper indium selenide) onthe release layer. The upper end of such a relatively group 1 rich layercan be approximately 25% group 1 by mole. The additional copper or othergroup 1 element tends to attach or incorporate more copper during theprecursor interaction. The crystallographic structure of a pure indiumselenide film varies with the ratio of indium to selenide in the film.But it is always irrespective of that ratio characterized by a hexagonalstacking of the selenide sub-lattices. A potential problem is that thecomposition layer desired in the end may have a different stackingstructure. Aluminum and copper can be alloyed can be alloyed on theGroup 1 sublattice sites in this structure. Gallium and germanium can bealloyed among the Group 3 lattice sites. Sulfur and selenide can bealloyed on the Group 6 sites. The prototypical compound for theseexamples is copper indium diselenide. And all of these compounds, ifthey have sufficient copper, will be characterized by face centeredcubic stacking of the selenide sublattice rather than hexagonal. Theidea of alloying Group 1 elements into the front surface (between therelease layer and the precursor bulk) is to create a part of that layerwhich will be transferred that is already characterized by the desiredFCC structure for the group 6 sublattice, which is the one that sulfurand selenide lie on. If one creates a very highly ordered layer, eventhough that layer may be very thin, it will act as a template for theregrowth and the restructuring of the underlying precursor layer ontothe template (from the hexagonal stacking into the FCC stacking).

A very highly ordered region at that top surface is desirable since thattop surface becomes the junction. A structure like this may be used toimplement bandgap-composition engineering, that is controlling theforbidden gap in the graded-composition layers. Thus, it can bedesirable to put in elements that substantially do not redistributeduring the reaction process. An example of a relatively static group 1element is aluminum. Aluminum is far less mobile than copper. By addingaluminum to the surface region in contact with the reusable tool, itwill stay there, and it will have the effect of increasing the width ofthe band gap in that region, which can be used to tailor the electronicproperties of the junction region itself. Further, it can be desirableto add sulfur to this region to tailor the properties of the junction.

By controlling the ratio of the different elements, the position of theelectrochemical potential can be controlled. The electrochemicalpotential at absolute zero is equivalent to and referred to byphysicists in general as the Fermi level.

By constraining the surface of the group 1 rich layer against therelease layer of the reusable tool, it can take on the surfacemorphology of the tool, which can be used to create a very smoothjunction, which is desirable from an electronic point of view becausethe voltage of the device is proportional to the logarithm of the ratioof the light-generated current to the recombination current. Therecombination current at the junction is directly proportional to thejunction's surface area. It is, therefore, desirable to minimize theactual contact area to allow the voltage to go up. To keep the actualcontact area minimized you should keep the junction interface flat.

The invention can include the use of a process facilitator such as asurfactant. The surfactant can be an alkali (e.g., sodium). Thesurfactant can be incorporated into one or both precursors as animpurity. The maximum local content of surfactant should not exceed thethreshold for precipitation of secondary phases (e.g., approximately0.5% by weight of sodium in the case of CIS and related materials). Thesurfactant lowers surface tension. The surfactant can improve diffusionrates, improve the crystallographic structure, defect properties and/orplanarity.

The sodium may prevent the formation of local defects which can lead toan undesirable crystallographic structure. The sodium tends to aggregateat the interface of the high copper region band the high indium region.It can be desirable to alloy the sodium during the deposition of theindium selenide layer to have a substantial sodium content near therelease layer. If a high copper layer is located between the releaselayer and an adjoining sodium impurity containing sublayer of the indiumselenide, the sodium impurity containing sublayer will ride on theinterface between the high indium and the high copper, and retard theincorporation of copper except at that interface. This can involveforming a junction crystallographic region first, and then incorporatingsodium behind that region. Aluminum can be included in the regionadjoining the release layer. The aluminum will be less mobile than thecopper. Sulfur can also be included in the region adjoining the releaselayer. Sulfur improves the defect properties at the junction. Whensodium is incorporated at a concentration low enough to preventprecipitation of sodium selenides, it will ride on that interface andcollect there. The copper being transported through will not crystallizeout; the copper will not initiate precipitation of another nucleus;until the copper hits that interface where the copper is already high,and it will displace the sodium, floating the sodium towards the meltsurface. Thus, the invention can include a release layer, then analuminum-copper-indium-gallium sulfo-solenide layer and then a sodiumcontaining layer, followed by the bulk of the first precursor layer.

The sodium should be introduced as an impurity rather than a separatelayer. The sodium should be delivered to one or both of the precursorlayers in a dilute form during the growth of the precursor layer(s). Thereason the sodium can move (can ride on the interface) may be that thesodium has lower solubility in the ternary compound (e.g., CIGS, whichis an alloy of two ternary compounds) than in the binary compound. Ifthe sodium is too concentrated, an undesirable a secondary phase mayprecipitate. The surfactant may work better if it is not thatconcentrated.

The invention can include incorporating the sodium as an impuritythroughout all of the first precursor layer and/or all of the secondprecursor layer. This can be desirable since some of the sodium may beleft behind in the crystallizing material layer as the primarysurfactant containing layer advances (floats) away from the releaselayer. Doping the sodium as an impurity throughout the first precursorlayer and/or the second precursor layer can be used to replace thatsodium which may be left behind. However, if the doping concentration ofthe sodium throughout the first precursor layer and/or the secondprecursor layer is too high, the advancing primary surfactant containinglayer may become too rich in sodium. If the sodium impurityconcentration layer becomes too high, undesirable secondary sodiumcontaining phases may precipitate within the crystallizing compositionlayer. Further, the concentration of the sodium impurity within theprimary sodium containing layer can change as a function of the floatvelocity. A high float velocity will tend to compress the primary sodiumcontaining layer. Again, if the sodium concentration is too high,undesirable secondary sodium containing phases may precipitate.Therefore, it may be desirable to control the float velocity to preventexcessive sodium build-up or, alternatively, increase the sodiumconcentration if it is too low.

All of the techniques described in the preceding example of a preferredembodiment of an approach for CIS synthesis do not need to be usedtogether in order to provide a superior alternative to existingapproaches. For example, the precursors described above could both bedeposited onto the molybdenum surface and the calcium fluoride-coatedsilicon substrate coated with a very thin film of CIS, CIGS, CIGSS, orACIGSS before the assembly is brought together under pressure. In eithercase, the use of calcium fluoride as an interlayer between theprecursors and the silicon serves the multiple functions of a releaselayer, a diffusion barrier to the thin film's elemental components, adielectric barrier preventing electrical current flow from the siliconsurface through the film during synthesis if a voltage bias is used, anda crystallographic template for the epitaxial growth of the film.

It should also be noted that the relative position of the precursorlayers described in the foregoing example is not essential. The copperselenium containing precursor layer could be initially deposited on therelease layer coated tool. The indium selenium containing precursorlayer could be initially deposited on the electrocoated substrate. Theauxiliary layers (the group 1 rich layer and the surfactant containinglayer) might then also need to be repositioned.

The use of just temperature and mechanical pressure to control thereaction trajectory of the film formation process would still besuperior to processes using only a single substrate because theinvention can prevent the loss of selenide during the reaction. Selenidevapor is not efficiently incorporated into films grown by conventionalco-deposition methods, leading to additional equipment and raw materialscost to avoid its deficiency in the product when such approaches areused, since inadequate selenide incorporation is known to yield CIS withpoor electronic properties for PV device applications. This avoidance ofthe need for additional equipment and/or raw materials can be a verysignificant advantage of the invention.

Another example of a partial implementation of the preceding example ofa preferred CIS embodiment would be to use that same method but withoutthe pressure exerted by the precursors. The temperature, theelectrostatic field, the template(s), the surfactants, the magneticfield and/or catalyst(s) would still be sufficient to drive theinteraction between the precursors, albeit with the possible loss ofvapor from the precursors and/or material layer, depending on thecomposition of these layers.

Another example of a partial implementation of the preceding example ofa preferred CIS embodiment would be to omit the template. The pressureexerted between the precursors, the electrostatic field, thesurfactant(s), the magnetic field and/or catalyst(s) would still besufficient to drive the interaction between the precursors. Many of thebenefits described here will still accrue in the situation where noappropriate epitaxial dielectric is available. For example, anon-epitaxial dielectric layer of aluminum oxide would still act as aneffective atomic diffusion and current barrier, but without the benefitsof transferring a desirable crystallographic orientation and grainstructure from the tool into the growing film.

Another example of a partial implementation of the preceding example ofa preferred CIS embodiment would be to omit the template. The pressureexerted between the precursors, the electrostatic field, thesurfactant(s), the magnetic field and/or catalyst(s) would still besufficient to drive the interaction between the precursors. Many of thebenefits described here will still accrue in the situation where noappropriate epitaxial dielectric is available. For example, anon-epitaxial dielectric layer of alumina oxide would still act as aneffective atomic diffusion and current barrier, but without the benefitsof transferring a desirable crystallographic orientation and grainstructure from the tool into the growing film.

Another example of a partial implementation of the preceding example ofa preferred CIS embodiment would be to omit the process facilitator(e.g., surfactant). The pressure exerted between the precursors, theelectrostatic field, the templates, the magnetic field and/orcatalyst(s) would still be sufficient to drive the interaction betweenthe precursors.

FIGS. 3A-3D shows an example of the synthesis of CIGSS absorber filmsfor PV device applications. In FIG. 3A, a reusable tool 310 is coupledto a (Ca,Sr)F₂ release layer 320. The (Ca,Sr)F₂ release layer 320 iscoupled to an (In,Ga)_(y)(S,Se)_(1-y) precursor layer 330. A compliantglass substrate 340 is coupled to a titanium/molybdenum electrode 345.The electrode 345 is coupled to a copper selenide precursor layer 350.In FIG. 3B, the (In,Ga)_(y)(S,Se)_(1-y) precursor layer 330 and thecopper selenide precursor layer 350 have been brought into intimatecontact. In FIG. 3C, a chemical reaction product layer 360 (CIGSS) hasresulted from the interaction. In FIG. 3D, the reusable tool 310 and the(Ca,Sr)F₂ release layer 320 have been moved away from the chemicalreaction product layer 360 which remains on the compliant glasssubstrate 340.

If the reusable tool's surface is made of silicon and the release layerof calcium fluoride, strontium fluoride, or alloys thereof (i.e.,(Ca,Sr)F₂), then the appropriate choice of alloy composition can providea surface for the deposition of an indium-gallium sulfo-selenideprecursor with virtually the same crystallographic symmetry at theirinterfaces and lattice constants throughout those layers, facilitatingthe epitaxial growth of a highly crystalline (In,Ga)_(y)(S,Se)_(1-y)composition layer when the precursor layers are brought into contact.Thus, the superior crystallinity of the solid phase precursor layer(pre-reaction product) resulting from the use of a crystallographicallycoherent tool and release layer will be retained during the formationreaction with the liquid phase precursor layer, leading to superiorcrystallinity in the resulting solid CIGSS absorber film, which is thereaction product.

The precursor layers shown in FIGS. 3A-3D are examples of precursorstructures, and may contain other chemical elements (e.g., for thesynthesis of compounds other than CIGSS as in this example). In additionto those primary compositional elements required to form the reactionproduct, impurities that act as surfactants in any particular materialsystem can also be incorporated. For example in the case of CIGSSsynthesis, it is preferable that at least one of these precursor layerscontains an alkali impurity such as sodium to facilitate the formationand stability of smooth, planar compositional interfaces during thereaction between the fluid and solid phases created by melting of one ofthe precursor layers after they are brought into contact with oneanother. Since the function of surfactants occurs at the interfacebetween the precursors and sublayers of different compositions, withinthose layers, the surfactant(s) may be initially distributed within oneor both of the precursors predominately at their respective freesurfaces. Alternatively, the surfactant(s) may be initially distributedbetween the release layer and its coupled precursor layer, especially ifa group I rich template layer is located between the surfactant and therelease layer. One consequence of this method of introducing asurfactant is that it will not be distributed predominately at the freesurface of the final reaction product film, in contrast to all otherreported methods. This can be an important advantage of the inventionsince sodium may be particularly undesirable near, or in, the junctionregion.

Each of the reactant precursor layers shown in FIGS. 3A-3D may itself begraded in composition or comprised of sublayers with differentcomposition. In particular, the relative amounts of indium, gallium,sulfur, and selenide may vary throughout the thickness of the(In,Ga)_(y)(S,Se)_(1-y) precursor layer but should be substantiallyuniform at any given depth within the layer at distinct points acrossthe layer. Such gradients may be modified by the product reactionprocess but should still result in a final product film with uniformaverage composition across the film, albeit possibly retaining vestigesof the initial depth-dependent composition gradient.

FIGS. 4A-4B show an example of applying an electrostatic field acrossthe two precursors. Referring to the upper subassembly of FIG. 4A, areusable tool 410 is coated with a release layer 420. The release layer420 should have a high dielectric constant and a high breakdown voltage.A (In,Ga)_(y)(S,Se)_(1-y) precursor layer 430 is coupled to the releaselayer 420. Referring to the lower subassembly of FIG. 4A, a compliantsubstrate 440 is coated with an electrode layer 445. A group 3containing adhesion layer 447 is coupled to the electrode layer 445. ACu_(x)Se_(1-x) precursor layer 450 is coupled to the group 3 containingadhesion layer 447. The group 3 containing adhesion layer 447 canfacilitate the wetting of the melted precursor. The group 3 containingadhesion layer 447 should stick to the electrode. The group 3 containingadhesion layer 447 should not melt, while the precursor layer 450 may.The parentheticals in FIG. 4A represent the voltage applied across theprecursor layers during the interaction of the precursor layers. Eachparenthetical includes a first value and a second value separated by acomma. The first value represents the electrostatic field configurationused to slow down the diffusion of copper. The second value representthe electrostatic field configuration used to speed up the diffusion ofcopper. In FIG. 4B, a CIGSS absorber layer 460 is shown coupled to aresidual group 3 containing adhesion layer 465. There are noparentheticals in FIG. 4B, since the interaction is complete noelectrostatic field is being applied. Needless to say, it can beadvantageous to switch off the electrostatic field before attempting tomove the reusable tool 410 relative to the compliant substrate 440.

Referring now to FIGS. 5A-5B, a template can be located within thesubassembly composed by the reusable tool and the(In,Ga)_(y)(S,Se)_(1-y) layer. This can be implemented by adding some ofthe copper required to achieve the desired overall composition into thepredominately (In,Ga)_(y)(S,Se)_(1-y) layer or a sublayer thereof. Forexample, a sublayer with an overall atomic ratio of copper to indiumplus gallium of about one-fifth (0.2≈[Cu]/([In]+[Ga])) to one-half maybe added at the precursor's interface with the release layer, at thatprecursor's free surface, or throughout its entire thickness.

FIGS. 5A-5B show an example of locating multiple templates next to theprecursors. Referring to the upper subassembly of FIG. 5A, a reusabletool 510 is coated with a release layer 520. As discussed above, whenthe release layer has a composition defining a crystalline structurethat matches the crystalline structure of the desired final film (e.g.,in the case of a CIGSS absorber layer (Ca,Sr)F₂), the release layer canfunction as a template. In addition to the template capability of therelease layer, this example features a (Al,Cu)(In,Ga)(S,Se) templatelayer 525 coupled to the release layer 520. A (In,Ga)_(y)(S,Se)_(1-y)precursor layer 530 is coupled to the (Al,Cu)(In,Ga)(S,Se) templatelayer 525. Referring to the lower subassembly of FIG. 5A, a compliantsubstrate 540 is coated with a titanium adhesion layer 542. An electrodelayer 545 is coupled to the titanium adhesion layer 542. A(Al,Cu)(In,Ga)(S,Se) template layer 547 is coupled to the electrodelayer 545. A Cu_(x)Se_(1-x) precursor layer 550 is coupled to the(Al,Cu)(In,Ga)(S,Se) template layer 547. In FIG. 5B, a CIGSS absorberlayer 560 is shown sandwiched between a first residual template layer570 and a second residual template layer 580. The first residualtemplate layer 570 corresponds to the (Al,Cu)(In,Ga)(S,Se) templatelayer 525. Similarly, the second residual template layer 580 correspondsto the (Al,Cu)(In,Ga)(S,Se) template layer 547. The titanium adhesionlayer 542 can remain largely undisturbed between the electrode layer andthe compliant substrate.

FIGS. 6A-6B show an example of locating multiple surfactant containinglayers within and/or next to the precursors. Referring to the uppersubassembly of FIG. 6A, a reusable tool 610 is coated with a releaselayer 620. An aluminum copper saturated layer 625 is coupled to therelease layer 620. A sodium containing layer 627 is coupled to thealuminum copper saturated layer 625. A (In,Ga)_(y)(S,Se)_(1-y) precursorlayer 630 is coupled to the sodium containing layer 627. In addition tothe surfactant capability of the sodium containing layer 627, a sodiumcontaining layer 633 is coupled to the (In,Ga)_(y)(S,Se)_(1-y) precursorlayer 630. While this example shows both of the sodium containing layers627 and 633, the invention does not require both, or even one, of theselayers. Referring to the lower subassembly of FIG. 6A, a compliantsubstrate 640 is coated with an electrode layer 645. A Cu_(x)Se_(1-x)precursor layer 650 is coupled to the electrode layer 645. In additionto the surfactant capability of the sodium containing layer 627, and thesodium containing layer 633, another sodium containing layer 655(Cu_(y)Se_(1-y):Na) is coupled to the Cu_(x)Se_(1-x) precursor layer650. While this example shows three sodium containing layers 627, 633and 655, the invention does not require all three, or two, or even one,of these layers. Of the three depicted sodium containing layers, thesodium containing layers 627 is preferred since it may more predictablyand controllably float down as diffused copper accumulates. Theaccumulation of diffused copper above the sodium containing layer 627 isdiscussed in more detail above. In FIG. 6B, a CIGSS absorber layer 660is shown sandwiched between a residual aluminum copper saturated layer675 and a collection layer 685. The residual aluminum copper saturatedlayer 675 corresponds to the aluminum copper saturated layer 625. Thecollection layer 685 is a zone for the collection of whatever is notincorporated in the absorber layer 660. The collection layer 685provides process tolerance. The region of the absorber layer 660 nearthe electrode layer 645 is an acceptable zone for the precipitation ofsecondary phases that contain excess reactants. By precipitating thesesecondary phases, they can be irreversibly bound in a tolerablelocation. The collection layer can be termed a gettering layer. Thecollection layer 685 can be utilized with other precursor-material layersystems, not just absorbers. If not in a kinetically limited regime, atthe growth interface there is an energetic barrier to furtherincorporation of that excess. The excess presence in the collection zone685 can include secondary copper containing phases (e.g., Cu₂Seprecipitates) and/or secondary sodium containing phases (e.g., NaInSe₂precipitates). The collection layer 685 can include residue from thesodium containing layer 625. The collection layer 685 can also includeresidue from the sodium containing layers 633 and 655 if copper from theCu_(x)Se_(1-x) precursor layer 650 does not overtake the sodium from thesodium containing layers 633 and 655 before the sodium from these layersreach the aluminum copper saturated layer 625. The collection layer 685can also include other undesirable phases and debris.

The substrate preferably presents at least one compliant surface. Thecompliant substrate may be formed for example of a polymeric materialsuch as polyimide, a relatively soft metal foil, or an alkali glass witha glass transition temperature near the desired processing temperature.In the latter case, the mechanical compliance that provides for intimatecontact between the thin (e.g., less than or equal to approximately 10microns) precursor layers results from softening of the glass near itsglass transition temperature. The compliant substrate need not beuniform in composition, and may itself be comprised both of a nominallyuniform, relatively rigid bulk with a thin compliant layer at or nearits interface with the electrode layer. A non-homogenous compositesubstrate can be structured where the melting point is lower near theinterface with the precursor. Such a layered structure can be created bychemical etching techniques that leave a porous surface structure or bythe deposition of an interfacial layer of another material. Theinterfacial layer of another material can include melting point loweringsubstances such as sodium and/or potassium. The interfacial layer ofanother material can include a colloidal dispersion of silica sodiumglass particles deposited by dipping or spraying methods. Other alkalismay be used provided that they have a lower glass transition (i.e.,softening) temperature. The higher sodium or potassium containingsilicates melt at a lower melting point than the lower sodium orpotassium containing glasses. By coating a rigid substrate, an intimatecontact between the two precursor layers can be facilitated. Without acompliant coating to facilitate intimate contact waves, ripples, ridgesand other kinds of surface features may prevent the two precursor layersfrom coming into intimate contact with one another. Of course, thesubstrate does not have to be compliant.

The metal electrode preferably includes molybdenum metal, but may be amultilayered structure including other metallic layers such as titanium.In this case, the titanium can be either sandwiched between molybdenumlayers as etch-stop layers or located at the back interface with thecompliant substrate in order to promote adhesion of the remainder of theelectrode with the compliant substrate.

The invention can include an optional adhesion layer between the copperselenide and the electrode. The adhesion layer between the copperselenide and the electrode can include a Group 3 element, (e.g.,gallium) or a group 3 containing compound (e.g., indium tellurium). Whenthe copper selenide melts into the form of liquid, it maybe desirable tohave a wetting layer there, and one of the best ways to create such awetting layer is to add a Group 3 element to actually form CIGS at thatback interface. As long as the dominant re-growth process occurs fromthe other interface, opposite the molten layer, the re-growth processmay transfer the crystallographic structure from that other interfaceinto the bulk. This depends on the relative growth rate in the twodirections. The relative growth rate can be modulated by the electricfields.

The invention can include the use of barrier layers. As noted above, therelease layer can simultaneously function as a barrier layer. It may bedesirable to create an epitaxial silicide barrier layer between thesilicon and the release layer, to prevent copper from getting into thesilicon. A copper diffusion barrier useful in conjunction with theinvention includes tungsten silicide. In order to get to the underlyingsilicon, copper needs to transport through the release layer. Therefore,one logical place to locate such a barrier can be at the interfacebetween the silicon and the release layer. It might be useful to haveanother optional barrier layer near the electrode. The invention caninclude a barrier layer between the electrode and its adherent precursorstructure, for example the copper selenide. Indium or gallium can beadded into the copper selenide layer to create an interfacial layer ofCIS or CIGS which would not be of high crystallographic quality, butwhich would adhere very strongly both to the copper selenide and theelectrode. The barrier layer at that interface between the copperselenide and the electrode would help to prevent diffusion of sodiumfrom a glass substrate into the reactant layer. However, one of theadvantages of the invention is that the alkali atoms in the compliantlayer may not have time to transport through the glass matrix into theelectrode layer. The invention can also include an optional sodiumbarrier layer between the compliant substrate and the electrode. With apolyimide surface it might be necessary to use titanium as a barrierand/or adhesion layer. Titanium is an effective adhesion layer inlayered systems.

While not being limited to any particular performance indicator ordiagnostic identifier, preferred embodiments of the invention can beidentified one at a time by testing for the presence of uniformcomposition at a given depth in the composition layer. The test for thepresence of uniform composition at a given depth in the compositionlayer can be carried out without undue experimentation by the use of asimple and conventional dynamic SIMS (secondary ion mass spectroscopy)experiment. Among the other ways in which to seek embodiments having theattribute of uniform composition at a given depth in the compositionlayer guidance toward the next preferred embodiment can be based on thepresence of uniform performance (e.g., electrical, photovoltaic,chemical, etc.).

Devices that Incorporate the Material Layers

Referring to FIG. 7, the invention can include devices that incorporatethe material layer(s). FIG. 7 depicts a photovoltaic device that isuseful as a solar cell for electric power generation. A glass substrate710 is coupled to an electrode 720. The electrode 720 is coupled to anabsorber layer 730. Examples of absorber layers are discussed above indetail and include CIS, CIGS, CISS, ACIS, ACIGSS and CIGSS.

A buffer layer 740 is coupled to the absorber layer 730. The bufferlayer 740 is sometimes inaccurately referred to as a passivating layer.A good buffer layer usable with the invention can include cadmiumsulfide, for example cadmium sulfide zinc oxide. Other substantiallynon-conducting buffer layers include indium oxides, indium selenides,cadmium sulfide, zinc selenide, and zinc oxide and alloys thereof.

A window layer 750 is coupled to the buffer layer 740. The transparentconducting window layer 750 provides lateral conductivity. Needless tosay, the window is transparent in order to get light to the absorber.And it has to be laterally conductive in order to get the electrons outand over to an external circuit via a grid line if present, or a busbar. The window functions as a front electrode. The invention can usezinc oxide which is optically transparent as the window. Alternatively,the invention can include using a conductive zinc oxide for the windowand a relatively non-conductive zinc oxide. In this case, thenon-conductive zinc oxide becomes part of the buffer layer. If thewindow layer that provides the lateral conductivity includes zinc oxide,it can be achieved with an electrical donor impurity, examples of whichare indium, gallium, aluminum or phosphorous.

An optional trace grid 760 is coupled to the window layer 750. If a gridis used, it can be a metallic bi-layer of nickel, in contact with thezinc oxide and then aluminum on top of the nickel. It is undesirable toput aluminum directly on zinc oxide since it will chemically react andform aluminum oxide which is insulating. The device includes an optionalencapsulating package 770 that can be made of a polymer (e.g., polyvinyl acetate block copolymer). The device can be coupled to a bus bar(not shown).

An antireflection layer is not necessary with these materials. Thebuffer layer acts as an anti-reflection coating. The stack of materialsdescribed has a graded index of refraction. The refractive index dropsfrom window to electrode. The refractive index of zinc oxide window islower than the index of the buffer which is lower than that of theabsorber. In this way, the structure builds in an anti-reflectioncharacteristic. A problem with anti-reflection coatings is, that the inthese particular type of devices, the enhancement in performance isusually not worth the extra cost.

Systems that Incorporate the Devices

Referring to FIG. 8, the invention can include systems that incorporatedevices that include the material layer(s). FIG. 8 depicts a mobileelectric power generating system. An array of solar cells 810 is coupledto a tracking subsystem 820. The array of solar cells 810 can be rotatedand tilted by the tracking subsystem 820 and is shown in an orthogonalposition for visual clarity. The tracking subsystem 820 can includeelectronics that include semiconductor components which include thematerial layer(s) described in detail above. The tracking subsystem 820is coupled to a vehicle 830. The vehicle 830 can include an electricpower storage subsystem such as a battery bank, a capacitor bank and/oran inductor bank that can include superconducting magnetic componentswhich include the material layer(s) described in detail above.

Equipment for Manufacturing the Material Layers

Two different generic manufacturing approaches described, of which eachcan implement the techniques of the invention. The first approach isdesigned to sequentially process substrates with a discrete tool and cantherefore be termed a “batch” process. The second approach can be termeda “continuous” process uses a continuous processing tool and either acontinuous series of discrete substrates or a continuously fed flexiblesheet substrate.

An example of a tool that can be used for discrete substrate processingis shown in FIGS. 9A-9B. FIGS. 9A-9B depict cross-sectional (FIG. 9B)and plane-view (FIG. 9A) schematic drawings of an exemplary discreteprocessing tool 910. A release layer 920 is coupled to the tool 910. Inthis example, a round silicon wafer is used as a reusable tool. Thisreusable tool has been patterned in cross-sectional relief to provide araised hexagonal surface. In this example, the release layer 920includes calcium fluoride. The raised surface of the layer 920 definesthe area of contact of the tool, and its release layer, and itsprecursor coating (first precursor), with the substrate, and itsprecursor coating (second precursor). The tool's precursor coating willbe brought into contact with the substrate's precursor coating andtransferred during the process of formation. The use of a hexagonalpattern is only one example. Better performance for PV applications canbe achieved by using geometrical patterns which can be tiled by multipleapplications of the tool(s) to cover substantially all of thesubstrate's surface (e.g., triangles, parallelagrams, etc.).

After the release layer 920 of the tool 910 has been coated with itsappropriate precursor layer it is placed in contact with the substratethat has been coated with the other reactant precursor. If the tool hasbeen already been preheated to the desired reaction temperature,pressure should be applied immediately. It may be preferable to preheatthe tool and substrate to an initially lower temperature so that theymay be brought into contact first and then rapidly heated while theircontact pressure is increased. The pressure can be increased byincreasing a mechanically applied force and/or by increasing an appliedelectrostatic field. The pressure can be similarly decreased.

One of the potential problems with using calcium fluoride as a releaselayer is that the material is mechanically soft. It may be desirable to,after transferring the product layer off of the release layer surface,recycle the release layer coated tool to a substantially highertemperature in order to get the release layer to smooth out, therebyimproving the surface of the release layer for subsequent re-depositionof a fresh precursor layer. If the tool lifetime becomes problematicusing a relatively soft material like calcium fluoride, it might bepreferable to use an extremely hard material, for example, diamond.

Irrespective of whether the specific material combination of silicon asthe reusable tool material and calcium fluoride, strontium fluorideand/or (Ca,Sr)F₂ as the release layer is used, it is desirable that thematerials used for these components be capable of sustaining the highprocessing temperatures of at least approximately 500° C., preferably atleast approximately 600° C., without excessive degradation of theirmechanical, crystallographic, and electrical properties.

One of the advantages of the invention is that most of the heat requiredto form a high-quality final layer can be provided by heat flow throughthe tool and release layer rather than by heating the compliantsubstrate. This permits the use of materials for the substrate thatwould not be stable if heated to such high temperatures for extendedperiods of time (e.g., plastics such as polyimide). Thus, the totalthermal budget for the process can be reduced by either very rapidheating (e.g., greater than or equal to approximately 50° C./second) ofthe tool after it is brought into contact with the substrate, or by verybrief contact (e.g., less than or equal to approximately 2 seconds,preferably less than or equal to approximately 0.5 seconds) between thepreheated tool and substrate (i.e., long enough for the material layercomposition formation to be substantially complete).

Rapid heating may be achieved by numerous methods including but notlimited to the following approaches. Rapid heating may be achieved byapplying an electrical bias to the silicon wafer while simultaneouslypassing a current pulse through the wafer laterally to rapidly heat it(this approach may require a holder for the tool designed to make atleast two electrical contacts on opposite edges of the wafer). Rapidheating may be achieved by bringing an electrically biased, heatedpiston into contact with the back side of the tool. Rapid heating may beachieved by heating the rear surface of the wafer radiatively to thereaction temperature while separately biasing the wafer via anelectrical contact to the wafer. Of course, these rapid heating methodscan be combined.

Referring to FIG. 10, an apparatus for implementing this process neednot necessarily handle each tool as a separate entity. Tools may, forexample, be placed together into an array on a larger platen, which isthen treated as a meta-tool in the same manner as described above. Forthis variation of the apparatus design it may be preferable to shape aplurality of individual tools as hexagon shaped wafers, rather thanproviding a hexagonal relief on a round silicon wafer, to define thecontact area between the meta-tool and substrate. Multiplestep-and-repeat transfer steps might be required to create aclose-packed tiled array of reactant product film areas over a largesubstrate, particularly if the ganged-wafer tool is itself not aclose-packed tiled array.

FIG. 10 depicts a tool-mounting platen 1010 used to gang togetherindividual hexagonal wafers 1020 (and half-wafers 1030). The platen 1010can provide parallel electrical contacts to these wafers forsimultaneous processing. The tool shown in FIG. 10 would enablesimultaneous formation of a material layer (e.g., chemical product film)over substantially a substrate's entire surface, even if the substratewere large. Substrates larger than the depicted meta-tool could also beaccommodated with a step and repeat approach. The individual wafers neednot necessarily be hexagonal, but could also be, for example, triangularor rectangular. The tool wafers need not necessarily be composed of asingle crystal, but could instead be multicrystalline.

The invention can include continuous substrate processing apparatus. Analternative to the use of multiple individual wafers in a planar arrayis shown in FIG. 11. FIG. 11 depicts a schematic drawing of an exemplarycontinuous processing apparatus to implement the reactive synthesis andsimultaneous transfer method of multinary compound formation.

A continuous substrate 1110 (web) passes under a rotating cylindricaltool 1120. A radiant heater 1130 is located within the tool 1120. Thetool 1120 and the radiant heater 1130 are located within a housing 1140.A series of deposition sources 1150 for the precursor that is carried bythe tool is also located within the housing 1140. Upstream from the tool1120 is a series of deposition sources 1160 for the precursor that iscarried by the substrate 1110. The sources 1160 are located within ahousing 1170. The tangental approach of the cylindrical tool 1120 maycause the pressure exerted on the precursors to ramp-up and thenramp-down. This can be a significant advantage in transport reactions.

FIG. 11 shows a cylindrical tool geometry. For CIS synthesis this typeof tool could be made of either a single continuous silicon tube¹⁶ ormultiple rectangular silicon slabs mounted onto a supporting tube, witheach rectangular slab then ground to create a cylindrical surface whenthe slabs abut one another. This type of tool is most useful forprocessing either a continuously fed flexible sheet or a continuousseries of discrete substrates.

In the case of the silicon tool and calcium fluoride release layerstructure, an alloy can be used to bond semicylindrical or arcuate toolsto a metal drum. This would permit piece-wise replacement of the silicontools, rather than having to replace all the tools on the whole drumwhich might be required if the drum is made of solid silicon. There aregood mechanical reasons to use a bonding alloy as well, such as thermalexpansion considerations. Further, it may be more cost-effective to makethe drum out of strips of silicon rather than a whole cylinder ofsilicon.

It is desirable that the release layer stay on the tool when thecomposition layer is transferred off the release layer. As noted above,the invention can include an optional adhesion layer between the tooland the release layer. The release layer can be part of the tool andpreferably remains part of the tool after separation. Whether such anoptional adhesion layer is needed depends on the material used for therelease layer and for the body of the tool. If the body of the tool, forexample is silicon, and the release layer, for example is calciumfluoride, there may be no need to introduce an adhesion layer in betweenthe two. The adhesion between those surfaces is by an epitaxialtransition that creates a chemical bond between the calcium fluoride andthe silicon, which sticks very well. However, other materialcombinations might benefit from such an optional adhesion layer.

The particular manufacturing process used for implementing the inventionshould be inexpensive and reproducible. Conveniently, the pressurizationaspect of the invention can be carried out by using any forceapplication method. It is preferred that the process be controllableover a wide range of pressures, most preferably within a short timedomain. For the manufacturing operation, it is an advantage to employ adirect mechanical technique.

However, the particular manufacturing process used for applyingpressurization is not essential to the invention as long as it providesthe described functionality. Normally those who make or use theinvention will select the manufacturing process based upon tooling andenergy requirements, the expected application requirements of the finalproduct, and the demands of the overall manufacturing process.

The particular apparatus used for the pressure applying apparatus shouldbe strong, serviceable and retoolable. Conveniently, the pressureapplying apparatus of the invention can be made of any heat resistantmaterial. It is preferred that the material be tough, corrosionresistant and amenable to cleaning.

However, the particular apparatus selected for applying pressure to thesubstrate(s) and/or tool(s) is not essential to the invention, as longas it provides the described function. Normally, those who make or usethe invention will select the best commercially available material basedupon the economics of cost and availability, the expected applicationrequirements of the final product, and the demands of the overallmanufacturing process.

The disclosed embodiments show platens or a roller and conveyor as thestructure for performing the function of applying pressure, but thestructure for applying pressure can be any other structure capable ofperforming the function of applying pressure, including, by way ofexample a hydraulic system, an expanding gas or even an isostaticworking fluid.

The electrostatic field aspect of the invention can be carried out byusing any voltage application technique. It is preferred that thevoltage application technique be controllable over a wide range ofvoltages, most preferably within a short time domain. However, theparticular technique used to apply the voltage is not essential to theinvention as long as it generates the described electrostatic field. Theapparatus used to apply the voltage can be made of any electricallyconductive material. It is preferred that the electrically conductivematerial be heat resistant, corrosion resistant and amenable tocleaning. However, the particular apparatus used to apply the voltage isnot essential to the invention as long as it is capable of generatingthe required field.

The particular deposition process used for providing the templatesshould be inexpensive and reproducible. It is preferred that the processfor applying the template be sputtering followed by plasma discharge,particle deposition, physical vapor deposition and/or chemical vapordeposition. However, the particular process used to deposit thetemplates is not essential to the invention so long as it provides atemplate possessing the described functionalities.

The particular process used to provide the surfactant as an impurityshould also be inexpensive and reproducible. It is preferred that thesurfactant impurity be provided by sputtering followed by plasmadischarge, particle deposition, physical vapor deposition and/orchemical vapor deposition. However, the particular process used forproviding the surfactant is not essential to the invention as long as itprovides a surfactant containing layer having the describedfunctionalities.

The invention can also utilize data processing methods that transformsignals from the precursor and/or product layers to control processvariables. For example, the invention can be combined withinstrumentation to obtain state variable information to actuateinterconnected discrete hardware elements. For instance, the inventioncan include the use of pressure, voltage, current and/or temperaturesensors to control pressure exerting and/or heating equipment. Thus, thepressure exerted and/or the heat applied can be varied (e.g., in timedomain) as a function of a state variable. Similarly, vacuum and/orcooling equipment may be provided and controlled.

The term layer, as used herein, is generically defined to include films,coatings and thicker structures. The term coating, as used herein, issubgenerically defined to include thin films, thick films and thickerstructures. The term composition, as used herein, is generically definedto include inorganic and organic substances such as, but not limited to,chemical reaction products and/or physical reaction products. The termselenide, as used herein is defined as a material that includes theelement selenium and does not include enough oxygen to precipitate aseparate selenate base; oxygen may be present in selenide. The termtool, as used herein, is defined as a substrate intended for re-use ormultiple use. The terms a or an, as used herein, are defined as one ormore than one. The term another, as used herein, is defined as at leasta second or more. The term plurality, as used herein, is defined as twoor more than two. The terms including and/or having, as used herein, aredefined as comprising (i.e., open language). The term coupled, as usedherein, is defined as connected, although not necessarily directly, andnot necessarily mechanically. The term approximately, as used herein, isdefined as at least close to a given value (e.g., preferably within 10%of, more preferably within 1% of, and most preferably within 0.1% of).The term substantially, as used herein, is defined as at leastapproaching a given state (e.g., preferably within 10% of, morepreferably within 1% of, and most preferably within 0.1% of). The termdeploying, as used herein, is defined as designing, building, shipping,installing and/or operating. The term means, as used herein, is definedas hardware, firmware and/or software for achieving a result. The termprogram or phrase computer program, as used herein, is defined as asequence of instructions designed for execution on a computer system. Aprogram, or computer program, may include a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, an applet, a serviet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer system.

Practical Applications of the Invention

A practical application of the invention that has value within thetechnological arts is the manufacture of photovoltaic devices such asabsorber films or electroluminescent phosphors. Further, the inventionis useful in conjunction with the fabrication of semiconductors (such asare used for the purpose of transistors), or in conjunction with thefabrication of superconductors (such as are used for the purpose magnetsor detectors), or the like. There are virtually innumerable uses for theinvention, all of which need not be detailed here.

Advantages of the Invention

Coating or film synthesis representing an embodiment of the invention,can be cost effective and advantageous for at least the followingreasons. The invention improves the control of defect properties. Theinvention improves quality and reduces costs compared to previousapproaches.

All the disclosed embodiments of the invention disclosed herein can bemade and used without undue experimentation in light of the disclosure.The invention is not limited by theoretical statements recited herein.Although the best mode of carrying out the invention contemplated by theinventor is disclosed, practice of the invention is not limited thereto.Accordingly, it will be appreciated by those skilled in the art that theinvention may be practiced otherwise than as specifically describedherein.

The individual components need not be formed in the disclosed shapes, orcombined in the disclosed configurations, but could be provided invirtually any shapes, and/or combined in virtually any configuration.Further, the individual components need not be fabricated from thedisclosed materials, but could be fabricated from virtually any suitablematerials. Further, homologous replacements may be substituted for thesubstances described herein. Further, variation may be made in the stepsor in the sequence of steps composing methods described herein.

Further, although the compositional layer described herein can be aseparate module, it will be manifest that the compositional layer may beintegrated into the device and/or system with which it is associated(e.g., a photovoltaic devices including the compositional layer as anabsorber between an electrode and a buffer layer). Furthermore, all thedisclosed elements and features of each disclosed embodiment can becombined with, or substituted for, the disclosed elements and featuresof every other disclosed embodiment except where such elements orfeatures are mutually exclusive.

It will be manifest that various substitutions, modifications, additionsand/or rearrangements of the features of the invention may be madewithout deviating from the spirit and/or scope of the underlyinginventive concept. It is deemed that the spirit and/or scope of theunderlying inventive concept as defined by the appended claims and theirequivalents cover all such substitutions, modifications, additionsand/or rearrangements.

The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” and/or “stepfor.” Subgeneric embodiments of the invention are delineated by theappended independent claims and their equivalents. Specific embodimentsof the invention are differentiated by the appended dependent claims andtheir equivalents.

References

1. L. L. Kazmerski, F. R. White, and G. K. Morgan, Appl. Phys. Lett. 29,268 (1976).

2. R. A. Mickelsen, U.S. Pat. No. 4,392,451 (1983).

3. R. A. Mickelsen and W. S. Chen, U.S. Pat. No. Re. 31,968 (1985).

4. R. A. Mickelsen, U.S. Pat. No. 4,523,051 (1985).

5. H. W. Schock, Appl. Surf. Sci. 92, 606 (1995).

6. M. A. Contreras, B. Egaas, K. Ramanathan, J. Hiltner, A.Swartzlander, F. Hasoon, and R. Noufi, Progr. PV 7, 311 (1999).

7. R. R. Arya, T. C. Lommasson, S. Wiedeman, L. Russell, S. Skibo, andJ. Fogleboch, in The Conference Record of the 23rd IEEE PhotovoltaicSpecialists Conference (Institute of Electrical and ElectronicEngineers, Louisville, Ky., 1993), 516.

8. G. E. Hassan, M. R. I. Ramadan, H. El-Labani, M. H. Badawi, S.Aboul-Enein, M. J. Carter, and R. Hill, Semicond. Sci. Technol. 9, 1255(1994).

9. V. Probst, F. Karg, J. Rimmasch, W. Riedl, W. Stetter, H. Harms, andEibl, in Materials Research Society Symposium Proceedings 426, SanFrancisco, Calif., 1996 (Materials Research Society), p. 165.

10. V. Kapur, B. Basol, and E. S. Tseng, Solar Cells 21, 65 (1987).

11. B. M. Basol and V. K. Kapur, in The Conference Record of the 22ndIEEE Photovoltaic Specialists Conference (Institute of Electrical andElectronic Engineers, Las Vegas, Nev., 1991), 893.

12. C. Guillen and J. Herrero, J. Electroch. Soc. 142, 1834 (1995).

13. C. Eberspacher, K. Pauls, and J. Serra, in Conference Record of the28th IEEE Photovoltaic Specialists Conference (Institute of Electricaland Electronic Engineers, Anchorage, 2000), 517.

14. C.-H. Chang, B. J. Stanbery, A. A. Morrone, A. Davydov, and T. J.Anderson, in MRS symposium proceedings 485, Boston, Mass., 1997(Materials Research Society), p. 163.

15. P. Teheran, G. Cediel, L. M. Caicedo, L. Cota, H. Leal, H. A.Rodrigue, and G. Gordillo, J. Crystal Growth 183, 352 (1998).

16. B. H. Mackintosh, M. P. Ouellette, M. D. Rosenblum, J. P. Kalejs,and B. P. Piwczyk, in Conference Record of the 28^(th) IEEE PhotovoltaicSpecialists Conference (Institute of Electrical and ElectronicEngineers, Anchorage, 2000), 46.

17. The Electrical Engineering Handbook, CRC Press, (Richard C. Dorf etal. eds.), 1993.

What is claimed is:
 1. A photovoltaic device made by a processcomprising: exerting a pressure between a first precursor layer that iscoupled to a first substrate and a second precursor layer that iscoupled to a second substrate; forming a composition layer and acollection layer located closer to the second substrate than the firstsubstrate; and moving the first substrate relative to the secondsubstrate, wherein the composition layer remains coupled to the secondsubstrate and the collection layer remains coupled to the secondsubstrate.
 2. An electrical power generation system comprising thephotovoltaic device of claim
 1. 3. An electronic device made by aprocess comprising: exerting a pressure between a first precursor layerthat is coupled to a first substrate and a second precursor layer thatis coupled to a second substrate; forming a composition layer and acollection layer located closer to the second substrate than the firstsubstrate; and moving the first substrate relative to the secondsubstrate, wherein the composition layer remains coupled to the secondsubstrate and the collection layer remains coupled to the secondsubstrate.
 4. A photodiode made by a process comprising: exerting apressure between a first precursor layer that is coupled to a firstsubstrate and a second precursor layer that is coupled to a secondsubstrate; forming a composition layer and a collection layer locatedcloser to the second substrate than the first substrate; and moving thefirst substrate relative to the second substrate, wherein thecomposition layer remains coupled to the second substrate and thecollection layer remains coupled to the second substrate.
 5. Acomposition prepared by a process comprising: exerting a pressurebetween a first precursor layer that is coupled to a first substrate anda second precursor layer that is coupled to a second substrate; formingthe composition and a collection layer located closer to the secondsubstrate than the first substrate; and moving the first substraterelative to the second substrate, wherein the composition remainscoupled to the second substrate and the collection layer remains coupledto the second substrate.
 6. A photovoltaic device comprising thecomposition of claim
 5. 7. An electrical power generation systemcomprising the photovoltaic device of claim
 6. 8. An electronic devicecomprising the composition of claim
 5. 9. A photodiode comprising thecomposition of claim
 5. 10. A photovoltaic device made by a processcomprising: exerting a pressure between a first precursor layer that iscoupled to a first substrate and a second precursor layer that iscoupled to a second substrate; forming a film formed of multinarycompounds and a collection layer located closer to the second substratethan the first substrate; and moving the first substrate relative to thesecond substrate, wherein the film remains coupled to the secondsubstrate and the collection layer remains coupled to the secondsubstrate.
 11. An electrical power generation system comprising thephotovoltaic device of claim
 10. 12. An electronic device made by aprocess comprising: exerting a pressure between a first precursor layerthat is coupled to a first substrate and a second precursor layer thatis coupled to a second substrate; forming a film formed of multinarycompounds and a collection layer located closer to the second substratethan the first substrate; and moving the first substrate relative to thesecond substrate, wherein the film remains coupled to the secondsubstrate and the collection layer remains coupled to the secondsubstrate.
 13. A photodiode made by a process comprising: exerting apressure between a first precursor layer that is coupled to a firstsubstrate and a second precursor layer that is coupled to a secondsubstrate; forming a film formed of multinary compounds and a collectionlayer located closer to the second substrate than the first substrate;and moving the first substrate relative to the second substrate, whereinthe film remains coupled to the second substrate and the collectionlayer remains coupled to the second substrate.
 14. A photovoltaic devicemade by a process comprising: exerting a pressure between a firstprecursor layer that is coupled to a first substrate and a secondprecursor layer that is coupled to a second substrate; forming a coatingand a collection layer located closer to the second substrate than thefirst substrate; and moving the first substrate relative to the secondsubstrate, wherein the coating remains coupled to the second substrateand the collection layer remains coupled to the second substrate.
 15. Anelectrical power generation system comprising the photovoltaic device ofclaim
 14. 16. An electronic device made by a process comprising:exerting a pressure between a first precursor layer that is coupled to afirst substrate and a second precursor layer that is coupled to a secondsubstrate; forming a coating and a collection layer located closer tothe second substrate than the first substrate; and moving the firstsubstrate relative to the second substrate, wherein the coating remainscoupled to the second substrate and the collection layer remains coupledto the second substrate.
 17. A photodiode made by a process comprising:exerting a pressure between a first precursor layer that is coupled to afirst substrate and a second precursor layer that is coupled to a secondsubstrate; forming a coating and a collection layer located closer tothe second substrate than the first substrate; and moving the firstsubstrate relative to the second substrate, wherein the coating remainscoupled to the second substrate and the collection layer remains coupledto the second substrate.
 18. The photovoltaic device of claim 1, whereinthe collection layer is located between the composition layer and thesecond substrate.
 19. The electronic device of claim 3, wherein thecollection layer is located between the composition layer and the secondsubstrate.
 20. The photodiode of claim 4, wherein the collection layeris located between the composition layer and the second substrate. 21.The composition of claim 5, wherein the collection layer is locatedbetween the composition and the second substrate.
 22. The photovoltaicdevice of claim 10, wherein the collection layer is located between thefilm and the second substrate.
 23. The electronic device of claim 12,wherein the collection layer is located between the film and the secondsubstrate.
 24. The photodiode of claim 13, wherein the collection layeris located between the film and the second substrate.
 25. Thephotovoltaic device of claim 14, wherein the collection layer is locatedbetween the coating and the second substrate.